Nonslumping, foamable polyorganosiloxane compositions containing organosiloxane graft copolymers

ABSTRACT

Moisture curable, foamable compositions that do not slump appreciably in the uncured state when applied on a vertical surface, consist essentially of an RTV elastomeric composition, from 10 to 50 weight percent of a liquified blowing agent and at least 12 weight percent finely divided filler. The RTV elastomeric composition comprises the product obtained by mixing at least two moisture curable polydiorganosiloxanes with an effective amount of a moisture reactive crosslinker. A graft copolymer derived from a liquid polydiorganosiloxane and an ethylenically unsaturated organic monomer constitutes from 5 to 80 weight percent of the polydiorganosiloxanes.

REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of copending application Ser.No. 664,913, filed Oct. 26, 1984.

BACKGROUND OF THE INVENTION Field of the Invention

This invention relates to polyorganosiloxane foams. More particularly,this invention relates to one-part, nonslumping foamablepolyorganosiloxane compositions that include liquified blowing agents.In the presence of atmospheric moisture and atmospheric pressure, thecompositions form foams that cure with a minimum of collapse to yielduseful, low density products.

It is known to prepare foams by introducing a gaseous blowing agent suchas compressed air into one-part, moisture curable polyorganosiloxanecompositions that are typically employed as room temperaturevulcanizable (RTV) sealants. A characteristic of known RTV compositionsis the long time period required for these compositions to cure to theextent that the foam becomes self supporting. One way to maintain thecellular structure of the initially produced foam during curing is toplace a flowable RTV polyorganosiloxane composition in a vacuum chamberfor a period of time sufficient to obtain a self-supporting foam. Thistechnique is taught by Modic and Boudreau in U.S. Pat. No. 4,368,279,which issued on Jan. 11, 1983.

While the use of vacuum during curing may be practical for machine madefoams such as slab stock and molded foams, this technique cannot be usedwhen the foam is formed within a cavity of a building or other locationswhere it is not feasible to maintain the foam under vacuum duringcuring. In addition, the necessity of mixing in a gaseous blowing agentat the time the foam is formed requires that mixing and aereatingequipment be transported to the location where the foam is to beinstalled. For some applications, particularly those requiringrelatively small amounts of foam at remote locations, such equipmentwould not be practical. In these instances it would be considerably moreconvenient to employ a one-component foamable composition, including ablowing agent, packaged in a container that can be easily transported tothe application site and which is capable of repeatedly dispensing thefoamable composition without the need for additional processing steps oringredients.

A second method for reducing the collapse of partially cured foamsprepared using RTV polyorganosiloxane compositions is to incorporatefillers such as silica and calcium carbonate. Filled RTV compositionshave been packaged in 2-compartment aerosol cans together with acompressed gas that supplies the pressure required to expel thecomposition from the can in addition to forming the cellular structureof the foam. One package foamable compositions are described in U.S.Pat. No. 4,229,548, which issued to Sattleger et al. on Oct. 21, 1980,and in German published application No. 2,911,971, which was publishedon Oct. 9, 1980. The cured foams are typically of relatively poorquality and characterized by average cell sizes larger than 2 mm,densities from 0.48 to 0.81 g./cc and relatively low foam height due todrainage of uncured or partially cured liquid from the cellularstructure of the foam during the curing process. The need to minimizecollapse of partially cured foams by the use of vacuum, by heating toaccelerate curing, by the addition of large amounts of fillers or byother means requiring additional processing steps may more than offsetthe advantages achieved by using foamable compositions packaged inportable containers such as aerosol cans.

A disadvantage of some of the uncured foamed compositions disclosed inthe Modic and Boudreau patent discussed hereinbefore is that thesecompositions will flow for a distance of several centimeters when placedon a vertical or sloping surface. This phenomenon is referred to as"slumping." This problem typically does not occur in highly filledcompositions containing a nonliquifiable blowing agent such as air.

The advantage of liquifiable blowing agents is their ability to functionas solvents while in liquified form in an aerosol container. Thissolvent action permits use of high molecular weight polymers that wouldotherwise be too viscous for use in compositions intended for dispensingfrom aerosol containers. High molecular weight polymers are desirablebecause their high viscosity minimizes drainage of liquid materials frompartially cured foams.

The present invention is based on the discovery that two majordisadvantages of prior art RTV foamable polyorganosiloxane compositions,namely relatively high density and foam collapse, can be reduced toacceptable levels and the slumping of uncured compositions can besubstantially reduced by including in the composition a relatively smallamount of filler, a liquified blowing agent and a class ofdiorganosiloxane graft copolymers described hereinafter. The resultantcured foams exhibit a desirable combination of low density, smallaverage cell size and high cell concentration.

SUMMARY OF THE INVENTION

The nonslumping, one-part foamable polyorganosiloxane compositions ofthis invention comprise an RTV sealant composition obtained by mixingtogether under anhydrous conditions a hydroxyl endblockeddiorganosiloxane polymer, a moisture reactive crosslinker, a filler, aliquified blowing agent, and a diorganosiloxane graft copolymer preparedby the peroxide catalyzed polymerization of an ethylenically unsaturatedorganic monomer in the presence of a hydroxyl-endblockedpolydiorganosiloxane.

DETAILED DESCRIPTION OF THE INVENTION

This invention provides a foamable composition that is stable whenconfined under superatmospheric pressure and when released into an areaunder atmospheric pressure forms a nonslumping moisture curable foam,said composition consisting essentially of the product obtained bymixing under substantially anhydrous conditions

(A) a moisture curable RTV elastomeric polyorganosiloxane compositioncomprising the product obtained by mixing in the absence of atmosphericmoisture at least one polydiorganosiloxane curable in the presence of amoisture reactive crosslinker, a moisture reactive crosslinker and anoptional curing catalyst, the amount of said crosslinker beingsufficient to cure said polymer;

(B) less than 12 percent by weight of said foamable composition, of afinely divided filler;

(C) from 10 to 50 percent by weight of said foamable composition of aliquified blowing agent; and

(D) from 5 to 80 percent, based on the combined weight of allpolydiorganosiloxanes present in said composition, of an organosiloxanegraft copolymer obtained by the peroxide catalyzed polymerization of atleast one ethylenically unsaturated organic monomer in the presence of aliquid, hydroxyl endblocked polydiorganosiloxane.

The feature that characterizes the present foamable compositions istheir ability to form nonslumping foams over a wide range of blowingagent concentrations using a minimum amount of filler. The graftcopolymers described hereinabove make it possible to form a nonslumpingfoam at the low concentration of filler and high blowing agent levelsrequired to obtain a low density foam. As used herein, "nonslumping"implies that the foamable composition will not flow more than about 1.5cm. when applied on a substantially vertical surface.

Moisture curable RTV elastomeric compositions, referred to hereinafteras (A), are a known class of materials that are typically prepared bycombining at least one polydiorganosiloxane with a moisture reactivecrosslinker under conditions that exclude atmospheric moisture. Optionalingredients such as fillers, curing catalysts, adhesion promoters,pigments and flame retarding agents can also be present.

The polydiorganosiloxanes contain a silicon-bonded hydroxyl group or atleast two hydrolyzable groups such as alkoxy at each of the two terminalpositions of the polymer molecules. Moisture curable RTV elastomericcompositions are sufficiently described in the prior art that a detaileddescription of these materials is not required in this specification.

For the purposes of this invention, it should suffice to say thathydroxyl endblocked polydiorganosiloxanes suitable for use in (A) can beprepared by the base catalyzed hydrolysis and polymerization of cyclicdiorganosiloxanes under controlled conditions to yield polymers of thedesired molecular weight.

The organic groups present on the silicon atoms of the diorganosiloxanepolymers include hydrocarbon radicals containing from 1 to 20 or morecarbon atoms. The carbon atoms are, in turn, bonded to hydrogen atoms orto other atoms, such as halogen, or groups of atoms that will notadversely affect the storage stability or curing of the present foamablecompositions.

The silicon-bonded hydrocarbon radicals in the diorganosiloxane polymersare preferably one or more of methyl, vinyl, phenyl and3,3,3-trifluoropropyl. This preference is based on the availability ofthe intermediates used to prepare these polymers. Polydimethylsiloxanesare particularly preferred.

The polydiorganosiloxane can contain one or more of the aforementionedsilicon-bonded hydrocarbon radicals in the form of repeating units suchas dimethylsiloxane, diphenylsiloxane, methylphenylsiloxane andmethyl-3,3,3-trifluoropropylsiloxane. Most preferably (A) includes atleast one polydimethylsiloxane of the general formula HO[Si(CH₃)₂ O]_(m)H where m has an average value of from 60 up to about 600.

In addition to diorganosiloxane units, the organosiloxane portions ofthe polymers can contain small amounts, typically less than 0.5% byweight, of monoorganosiloxy, triorganosiloxy and SiO_(4/2) units. Theseadditional units result from impurities present in the startingmaterials or intermediates used to prepare the polymer. The molar ratioof hydrocarbon radicals to silicon atoms is preferably from 1.98 to2.01.

Foamable compositions containing less than about 12% by weight of afinely divided filler and more than about 10% by weight of a liquifiedblowing agent are in most instances too flowable to form a nonslumpingfoam, however compositions of this type are particularly preferredbecause they typically produce lower density foams having a highconcentration of uniformly small cells, i.e. cells having diameters of 2mm or less at a concentration of at least 4 per linear centimeter. Byincluding in the compositions from 5 to 80%, based on the combinedweight of all organosiloxane polymers, of an organosiloxane graftpolymer described in detail hereinbelow, the compositions can be madenonslumping. The concentration range of graft copolymer that is optimumfor a particular composition will be dependent at least in part on theconcentrations of silica and liquid blowing agent. This range can bedetermined with a minimum of experimentation by those skilled in the artusing the examples contained hereinafter as a guide.

Because the degree of slump exhibited by a particular foamablecomposition is dependent upon a number of parameters other than theconcentrations of filler and blowing agent, the range within which thegraft copolymer is useful for imparting nonslumping properties to agiven composition may vary slightly from those defined hereinbefore andin the accompanying claims. Parameters which effect slump include thetype and particle size of the filler and the viscosity of the moisturecurable organosiloxane composition, referred to hereinbefore as (A).

The organosiloxane graft copolymers that contribute to the nonslumpingnature of the foamable compositions of this invention can be prepared bythe peroxide catalyzed polymerization of ethylenically unsaturatedorganic compounds in the presence of liquid hydroxyl endblockedpolydiorganosiloxanes. A preferred class of graft copolymers isdescribed in U.S. Pat. No. 3,555,109, which issued to J. C. Getson onJan. 12, 1971. This patent is hereby incorporated herein by reference asa teaching of suitable organosiloxane graft copolymers.

The graft copolymers disclosed by Getson are characterized by thepresence of rod-shaped particles measuring from 5 to 500 micrometers inlength. The copolymers are prepared by reacting a mixture containingfrom 20 to 50% by weight of a substantially linear hydroxyl endblockedpolydiorganosiloxane exhibiting a viscosity of up to 6 Pa.s at 25° C.and from 50 to 80% by weight of one or more olefinically unsaturatedorganic monomers such as styrene, ethylene and esters of acrylic andmethacrylic acids. The reactants are combined with an organic peroxidecatalyst and the resulting mixture is stirred at a rate sufficient toproduce rod-shaped particles of the desired size range. The relationshipbetween particle size and shear rate is discussed in this patent.

A preferred graft copolymer composition is a hydroxyl terminatedpolydimethylsiloxane containing grafted styrene and butyl acrylateunits. This copolymer is available as Silgan® H-622 from SWS SiliconesCorporation. Because a high concentration of graft copolymer mayadversely affect certain desirable properties such as flame retardancyand weatherability exhibited by the cured foam, the concentration ofgraft copolymer should preferably not exceed about 40 weight% of thediorganosiloxane polymers in the foamable composition.

The combination of diorganosiloxane polymers in the foamable compositionexhibits a viscosity of from 0.05 to 100 Pa.s at 25° C. Preferably thisrange is from 0.1 to 15 Pa.s. Within this preferred range, optimumcombinations of practical dispensing rates for the composition and goodstability of the foam during curing are achieved.

The diorganosiloxane polymer portion of (A) typically constitutes from10 to 90% by weight of the entire foamable composition of thisinvention, exclusive of the liquified blowing agent. Preferably thisvalue is from 15 to 75%.

The moisture reactive crosslinker portion of (A) can be anypolyfunctional organosilicon material that will react withhydroxyl-containing polyorganosiloxanes at room temperature in thepresence of atmospheric moisture to form cured compositions. One classof suitable crosslinkers includes silanes of the general formula R_(n) ¹SiX_(4-n) where R¹ represents a monovalent hydrocarbon radical, X is ahydrolyzable group and the average value of n is less than 2 but greaterthan zero. X can be, for example, acyloxy such as acetoxy; alkoxy suchas methoxy; ketoximo of the formula --ON═CR₂ ² where each R² isindividually alkyl containing from 1 to 4 carbon atoms and is preferablymethyl or ethyl; aminoxy of the formula --ONR₂ ² ; or amido of theformula --N(R³)C(O)R² where R³ is hydrogen or R². Alternatively, X canrepresent two or more of the foregoing groups.

To ensure compatibility between the crosslinker and the polymer portionof (A), R¹ preferably represents a vinyl or a lower alkyl radical whenthe polymer portion of (A) consists essentially ofpolydimethylsiloxanes.

In place of, or in addition to the foregoing silanes, the crosslinkercan include partial hydrolysis products of these silanes or siloxanescontaining at least three silicon-bonded X groups per molecule.

Preferred crosslinkers for use in (A) include silanes where R¹represents methyl or vinyl and X represents --OC(O)CH₃, --ON(C₂ H₅)₂,--ON═C(CH₃)(C₂ H₅) or --OCH₃.

The crosslinker should be one that rapidly produces a cured foam. Theconcentration of crosslinker should be sufficient to provide a storagestable composition. To achieve storage stability, the molar ratio ofhydrolyzable groups present in the crosslinker, represented by X in theforegoing formula, to the hydroxyl groups present in the ingredientsused to prepare the foamable composition should be greater than 2:1. Amolar ratio of at least 3:1 is preferred.

The preferred crosslinkers described hereinbefore are typically used atconcentration levels of from about 0.1 to about 10 parts by weight per100 parts by weight of the diorganosiloxane polymer portion of (A).

The prior art teaches the relative reactivities of various crosslinkersfor RTV compositions and catalysts that can be employed to increasethese reactivities. Selection of an appropriate crosslinker andcatalyst, if required, can be accomplished with at most a minimum ofexperimentation by those skilled in the art using available information.Useful catalysts include inorganic and organic tin compounds, such asstannous octoate and dibutyltin dilaurate, and titanium compounds. It isknown that (1) crosslinkers containing aminoxy groups of the formula(ONR₂ ²), where R² is defined hereinbefore, as the hydrolyzable grouptypically do not require catalysts, and (2) titanium compounds,particularly chelated titanium compounds, effectively catalyze thereaction between silicon-bonded hydroxyl and silicon-bonded alkoxygroups in the presence of atmospheric moisture.

When alkoxysilanes are used as the crosslinker, the present compositionscan optionally include any of the known hydroxyl group scavengers thatare disclosed, for example, in U.S. Pat. No. 4,395,526, which issued toChung on Jan. 3, 1984, and is incorporated herein by reference.

The filler portion, (B), of the present foamable compositions, assistsin maintaining the cellular structure of the froth produced by theaction of the blowing agent within the foamable composition until thecomposition has cured sufficiently to become self supporting. In theabsence of the organosiloxane graft copolymers described hereinbefore,the relatively low filler concentration is not effective for reducingslumping using the large amount of blowing agent required to producefoams with densities less than about 0.6 g./cc.

Any of the finely divided reinforcing and nonreinforcing fillerstypically used in polyorganosiloxane compositions can be present in thefoamable compositions of this invention. These fillers include silica,quartz, diatomaceous earth, metal oxides such as iron oxide and metalcarbonates such as calcium carbonate. Finely divided forms of silicasuch as fume and precipitated silicas are preferred based on thedesirable properties these fillers impart to the final cured product.Fume and precipitated silicas typically have surface areas greater thanabout 100 m² /g.

The filler is present at a concentration of less than 12 percent byweight, based on the weight of the foamable composition. At higherconcentrations the properties of the cured foam, particularly densityand the ability of the foamable composition to be readily and uniformlydispensed from an aerosol container, are adversely affected.

Finely divided silica fillers used in polyorganosiloxane compositionsare often treated with relatively low molecular weight, liquid hydroxylcontaining organic or organosilicon compounds to prevent a phenomenonreferred to in the art as "crepe-hardening". The filler particles can betreated before being added to the composition or the particles can betreated "in situ" by having a suitable treating material present as aningredient in the compositions. Known filler treating agents include lowmolecular weight hydroxyl-endblocked polydiorganosiloxanes. The organicradicals present on silicon are lower alkyl such as methyl or vinyl,aryl radicals such as phenyl, and radicals such as3,3,3-trifluoropropyl.

The foamable polyorganosiloxane compositions of this invention areconverted to foams by the action of a liquifiable blowing agent (C). Theblowing agent is a gas under atmospheric pressure and temperatures aboveabout 20° C., is liquified under the superatmospheric pressure used topackage and store the present foamable compositions and is both miscibleand unreactive with the other ingredients of the composition. When thecomposition is released from the storage container, it is converted to afroth by volatilization of the blowing agent. The froth gradually curesto a solid, elastomeric foam.

Suitable liquifiable blowing agents include aliphatic hydrocarbonscontaining three or four carbon atoms. Butane, isobutane and mixtures ofisobutane and propane are particularly preferred on the basis of theircost and availability. Chlorofluorocarbons such astrifluorochloromethane will function as blowing agents but in somecountries are considered undesirable for ecological reasons.

Ingredient (C) constitutes from about 10 to about 50% of the weight ofthe entire foamable composition. The optimum concentration range isdependent upon a number of variables, the most influential of whichappears to be the viscosity of the foamable composition, which is, inturn, to a large extent dependent upon the viscosity of (A) and theamount of filler(s) present.

The optimum concentration of (C) is one that will provide the bestbalance between stability of the froth during curing, a sufficientlyrapid discharge rate of the composition from the container in which itis stored and a relatively low density cured foam.

Too much blowing agent will produce a "slumping" foam in the absence ofsufficient filler and/or organosiloxane graft copolymer. Too low aconcentration of blowing agent in a viscous composition will typicallyyield a high density foam. For preferred foamable compositions such asthose examplified hereinafter, the concentration of blowing agent isfrom 10 to 30%, based on the weight of the entire foamable composition.

The present compositions are preferably packaged in a 2-compartmentaerosol container wherein only one compartment is equipped with adispensing valve and contains the foamable composition and blowingagent. The second compartment is separated from the first by means of apiston or a compressible container and is filled with a propellant thatcan be of the same composition as the blowing agent or can be a morevolatile material. The propellant provides the additional pressurerequired to increase the rate at which a foamable composition can bedispensed from the pressurized container. Two compartment aerosol cansare known in the art and can be equipped with any of the known types ofaerosol valves.

All other conditions being equal, the maximum rate at which a foamablecomposition of this invention can be dispensed from a pressurizedcontainer and the rate at which liquid materials will drain duringcuring of the foam are both inversely proportional to the viscosity ofthe foamable composition. To obtain useful foams the presentcompositions in the absence of blowing agent should have the consistencyof a thick paste.

The foamable compositions of this invention can be prepared by packagingthe foregoing ingredients, (A), (B), (C), and (D) together with any ofthe optional additives discussed hereinbelow, under substantiallyanhydrous conditions in a moisture-tight container, such as an aerosolcan, that is capable of withstanding the pressure exerted by theliquified blowing agent and any propellant employed.

In accordance with one such preparative method, the polymer portion of(A), graft copolymer, filler(s) and any optional additives such aspigments, adhesion promoters and flame-retarding agents are blended tohomogeneity before being combined and blended with the crosslinkerportion of (A) and any curing catalyst under conditions that avoidcontact between these ingredients and atmospheric moisture. Theresultant composition is then transferred into a pressurizablecontainer, such as a two-compartment aerosol can, that is equipped witha dispensing valve. The desired amount of liquified blowing agent (C) isthen introduced into the container by appropriate means, usually throughthe dispensing valve or directly into the container just prior tosealing it, and the container is shaken to uniformly disperse theblowing agent throughout the composition. Methods and equipment forpackaging moisture-sensitive materials together with liquifiedpropellants such as isobutane in pressurized containers are well knownin the art and do not form part of this invention.

The pressurized containers used to package the foamable compositions areequipped with valves wherein the passages through which the compositionflows are of sufficient diameter to permit discharge of the compositionat a sufficiently rapid rate to form a useful foam. If the compositionwill be dispensed in portions over a period of several days or weeks,those passages within the valve and spray head that are exposed toatmospheric moisture should be capable of being sealed to minimizecontact with atmospheric moisture and resultant curing of foamablecomposition remaining in these passages. It is desirable that thepassages be sufficiently large in diameter to facilitate removal ofcured material.

Preferably the valves are of the toggle type recommended for dispensingrelatively viscous, foamable materials such as whipped cream. Mostpreferably the discharge tube and valve body are combined in a singlemember that is held in place by an elastomeric valve seat. One or moreopenings in the valve body are normally closed off by contact with theseat. Displacement of the discharge tube by finger pressure moves theopening(s) in the valve body away from the seat, thereby allowing thecontents of the pressurized container to flow into the valve body andthrough the discharge tube.

Those types of aerosol valves wherein the valve body and spray head areseparate units and the valve is equipped with a spring loaded piston,may be suitable for use with some of the less viscous foamablecompositions of this invention.

For large scale foam preparations where storage is not required, amixture of (A), (B) and (D) together with any other ingredients isdispensed from one container and the liquified blowing agent (C) isdispensed from a pressurized storage container. The ingredients arecombined in a suitable pressurizable mixing head and the resultant foamis dispensed at the desired location.

Preferred foamable compositions of this invention are stable for periodsof up to six months or more when stored in pressure-tight containersthat exclude atmospheric moisture.

Cured foams prepared using the compositions of this invention aretypically of the closed cell type. The size of the cells in the foamwill typically be less than 4 mm in diameter. Preferably the cells willrange from 0.2 to 2 mm in diameter and the cell concentration istypically greater than 4 per linear cm.

The present foams can be used in many applications where it is desirableto utilize the unique properties of moisture curable polyorganosiloxaneelastomers in a lower density material. The lower density of the foamsrelative to the corresponding noncellular elastomers makes it possibleto cover a larger area with the same weight of material. An additionaladvantage is the insulating properties provided by the closed cellstructure of the foam.

The ability of the present foamable compositions to remain stable in apressurized container makes it possible to combine in a single, portablepackage such as an aerosol container, all of the ingredients required toform a moisture curable foam. The package can then be transported to thelocation where the foam is to be applied rather than having to transportthe individual ingredients to the location, combine them in the requiredamounts, and prepare a homogeneous composition just prior to forming thefoam. This is particularly advantageous in those instances whenrelatively small amounts of foam are dispensed over a relatively longperiod of time.

The following example discloses a preferred embodiment of the presentfoamable compositions and should not be interpreted as limiting thescope of the accompanying claims. All parts and percentages are byweight unless otherwise indicated.

EXAMPLE 1

This example demonstrates the ability of a preferred organosiloxanegraft copolymer to produce a nonslumping foam at the relatively lowlevels of silica and high concentration of blowing agent required toobtain a low density foam.

Three foamable compositions were prepared to evaluate the effect offiller and blowing agent concentrations on slump. The compositions wereprepared using a Sem Kit® tube (available from Semco, Inc., Division ofProducts Research and Chemical Corp., Glendale, Calif.). This device isa cylinder formed from polyethylene, resembles a tube commonly used topackage caulking compounds and incorporates means for adding ingredientsand stirring the contents of the tube in the absence of moisture.

One of the compositions (I) was prepared by blending together 100 partsof a hydroxyl-terminated polydimethylsiloxane exhibiting a viscosity ofabout 13 Pa.s at 25° C., 15 parts of a polydimethylsiloxane graftcopolymer, 12 parts of fume silica (MS-7 from Cab-O-Sil Corporation), 3parts of a hydroxyl-terminated polymethylphenylsiloxane containing 4.5weight percent of silicon-bonded hydroxyl groups and 1.75 parts ofpartially hydrolyzed H₂ N(CH₂)₂ N(H)CH₂ CH₂ CH₂ Si(OCH₃)₃ as an adhesionpromoter. The resultant mixture was placed in the Sem Kit tube anddegassed under reduced pressure following which 10 parts of CH₃Si[ON═C(CH₃)(C₂ H₅)]₃ and 0.24 part of dibutyltin dilaurate were added,and the resultant composition was mixed for 3 minutes. The compositionwas then transferred into the flexible inner container of a Sepro®aerosol can, available from The Continental Group, Inc. A valve assemblyproviding access to the flexible container was attached to the can bycrimping and the contents of the inner container were degassed. Sixparts of a liquified gas containing 80 weight percent isobutane and 20weight percent propane were introduced into the outer compartment of thecan and an amount of liquified isobutane equivalent to 17 percent byweight of the total foamable composition was introduced into the innercontainer through the valve. The can was then placed on a mechanicalshaker for about 16 hours to distribute the isobutane blowing agentthroughout the foamable composition. The graft copolymer used isreported to have been obtained by polymerizing styrene and butylacrylate in the presence of a hydroxyl endblocked polydimethylsiloxaneand a peroxide catalyst. The copolymer is available as Silgan® H622 fromSWS Silicones Corporation, Adrian, Mich.

A second composition (II) that did not contain any Silgan® H622 wasprepared as described in the first part of this Example using 100 partsof the hydroxyl endblocked polydimethylsiloxane, 3.45 of thepolymethylphenylsiloxane, 11.5 parts of silica, 8 parts of the samecrosslinker, 0.2 part of dibutyltin dilaurate and 38%, based on thetotal composition weight, of isobutane. A third composition (III) wasprepared in the same manner using 100 parts of the polydimethylsiloxane,6 parts of the polymethylphenylsiloxane, 20 parts of silica, 10 parts ofthe same crosslinker, 0.2 part of dibutyltin dilaurate, and 20%, basedon total composition weight, of isobutane.

Foams were prepared by discharging a portion of each of these foamablecompositions into a vertically oriented aluminum channel measuring 0.63cm in width and 0.63 cm in depth. The walls and floor of the channelwere at right angles with respect to one another. The distance which thecomposition flowed in the channel during the five minute interval afterbeing dispensed from the container was recorded as "slump."

                  TABLE 1                                                         ______________________________________                                                 Silica   Isobutane                                                                              Silgan ®                                                (%       (%       (%     Density                                                                              Slump                                Composition                                                                            by Wt.)  by Wt.)  by Wt.)                                                                              (g./cc)                                                                              (cm.)                                ______________________________________                                        I        7        17       9      0.53   1.3                                  II (control)                                                                           6        38       0      0.49   7.6                                  III      12       20       0      0.60   0                                    ______________________________________                                    

These data demonstrate that the presence of the graft copolymer in Ireduces by 40 percent the amount of silica required to reduce slumpingof a foamable composition thereby reducing the density of the curedfoam.

EXAMPLE 2

The difference in flow properties between a foamable compositioncontaining a liquified hydrocarbon mixture and one containingnonliquified air, was demonstrated using a moisture curable compositioncontaining the following ingredients:

30.9 parts of a hydroxyl endblocked polydimethylsiloxane exhibiting aviscosity of 50 Pa.s at 25° C.,

11 parts of a trimethylsiloxy endblocked polydimethylsiloxane exhibitinga viscosity of 1 Pa.s at 25° C.,

50 parts of finely divided calcium carbonate,

4 parts of fume silica,

4.09 parts of methyltrimethoxysilane,

0.0004 part of dibutyltin dilaurate.

The two polydimethylsiloxanes, calcium carbonate and silica were blendedtogether in a Sem Kit® tube described in Example 1 and combined with themethyltrimethoxysilane and dibutyltin dilaurate under conditions thatexcluded atmospheric moisture. The resultant composition was transferredinto the flexible inner containers of four 2-compartment Sepro® aerosolcans. The cans were then sealed using a cap equipped with a valve havingaccess to the inner container. The outer compartments of two of theSepro cans were charged with air to a pressure of 932 kPa. The outercompartments of the remaining two cans were each charged with 18 partsof a mixture containing 20 weight percent propane and 80 weight percentisobutane.

A foamable composition was also packaged in two modified Sepro canswherein the original inner container was replaced with one formed frompolyethylene. The moisture curable composition described in the firstpart of this example was placed in the inner container and the outercompartment was charged with 27 parts of a mixture containing 20 weightpercent propane and 80 weight percent isobutane.

The use of compressed air as a propellant and blowing agent for moisturecurable polyorganosiloxane compositions stored in two-compartmentaerosol containers is taught in West German published application No.2,911,971. The air, originally present only in the outer compartment,gradually diffused through the polyethylene liner into thepolyorganosiloxane composition located in the inner compartment of theaerosol container.

The four foamable compositions in the unmodified Sepro cans remainedunder ambient conditions for 9 weeks to allow a portion of thepropellant in the outer compartment to diffuse into the innercompartment containing the polyorganosiloxane composition. Thecompositions in the two modified cans with the polyethylene innercompartment were stored for 61/2 weeks prior to being dispensed.

The density and slump exhibited by the foams obtained from the foregoingcompositions are recorded in the following table. The values representthe average of the two samples of each type that were evaluated.

    ______________________________________                                                              Density     Slump                                       Can Type   Propellant (g/cc)      (cm.)                                       ______________________________________                                        Unmodified Propane/    1.1 ± 0.1.sup.(1)                                                                     0.sup.(1)                                   Sepro      Isobutane                                                          Unmodified Air         0.92 ± 0.02.sup.(1)                                                                   0.sup.(1)                                   Sepro                                                                         Modified   Propane/   0.83 ± 0.1.sup.(2)                                                                       7.6.sup.(2)                               Sepro.sup.(3)                                                                            Isobutane                                                          ______________________________________                                         .sup.(1) Composition stored for 9 weeks prior to being dispensed              .sup.(2) Composition stored for 61/2 weeks prior to being dispensed           .sup.(3) Original inner container replaced with polyethylene container.  

The density values for the foam obtained using air and the foam obtainedfrom the modified container are similar, indicating that thecompositions contained equivalent volumes of vaporized blowing agent.The foam obtained using air as the blowing agent did not slump while theone using the liquifiable blowing agent slumped considerably andrequires the graft copolymer of this invention to reduce slumping. Theprior art composition containing air as the blowing agent isconsiderably less flowable and does not require a graft copolymer toachieve a nonslumping character. The foregoing data demonstrate thatchoice of a liquifiable or nonliquifiable blowing agent has a profoundeffect on the flow properties of otherwise identical uncuredorganosiloxane compositions.

That which is claimed is:
 1. A foamable composition which is stable whenconfined under superatmospheric pressure and when released into an areaunder atmospheric pressure forms a nonslumping, moisture-curable foam,said composition consisting essentially of the product obtained bymixing under substantially anhydrous conditions(A) a moisture-curableRTV elastomeric organosiloxane composition comprising the productobtained by mixing in the absence of atmospheric moisture at least onepolydiorganosiloxane curable in the presence of a moisture reactivecrosslinker, a moisture reactive crosslinker and, optionally, a curingcatalyst, the amount of said crosslinker being sufficient to cure saidpolymer; (B) less than 12 percent by weight, based on the weight of saidfoamable composition of a finely divided filler; (C) from 10 to 50percent by weight of said foamable composition, of a liquified blowingagent sufficient to form a foam following release of said compositioninto an area under atmospheric pressure; and (D) from 5 to 80 percent,based on the combined weight of all diorganosiloxane polymers present insaid composition, of an organosiloxane graft copolymer obtained by theperoxide catalyst polymerization of at least one ethylenicallyunsaturated organic monomer in the presence of a liquid, hydroxylendblocked polydiorganosiloxane.
 2. A composition according to claim 1where the mixture of all polydiorganosiloxanes and said graft copolymerexhibits a viscosity of from 0.05 to 100 Pa.s at 25° C.
 3. A compositionaccording to claim 1 where the polydiorganosiloxane portion of (A) is ahydroxyl endblocked polydimethylsiloxane.
 4. A composition according toclaim 1 where said crosslinker comprises a silane of the general formulaR_(n) ¹ SiX_(4-n), a partial hydrolyzate thereof, or a siloxanecontaining at least three silicon-bonded X groups per molecule, where R¹is a monovalent hydrocarbon radical, X is a hydrolyzable group and theaverage value of n is less than 2 and greater than zero.
 5. Acomposition according to claim 4 where R¹ is methyl or vinyl, X isacyloxy, alkoxy, ketoximo, --ONR₂ ² where R² represents identical ordifferent alkyl radicals containing from 1 to 4 carbon atoms, or--N(R³)C(O)R², where R³ is hydrogen or alkyl selected from the samegroup as R².
 6. A composition according to claim 4 where X is--OC(O)CH₃, --ON(C₂ H₅)₂, --ON═C(CH₃)(C₂ H₅) or --OCH₃.
 7. A compositionaccording to claim 4 where the molar ratio of X groups to the totalnumber of hydroxyl groups in said composition is at least 3:1,respectively.
 8. A composition according to claim 1 where said curingcatalyst is an organic or inorganic tin compound or a titanium compound.9. A composition according to claim 1 where said composition is packagedin a container under superatmospheric pressure and substantiallyanhydrous conditions.
 10. A composition according to claim 1 where saidfiller is silica and said composition contains a treating agent for saidsilica.
 11. A composition according to claim 10 where said treatingagent is a liquid hydroxyl endblocked polydiorganosiloxane.